High aspect ratio etch with combination mask

ABSTRACT

A method for etching features in a stack is provided. A combination hardmask is formed by forming a first hardmask layer comprising carbon or silicon oxide over the stack, forming a second hardmask layer comprising metal over the first hardmask layer, and patterning the first and second hardmask layers. The stack is etched through the combination hardmask.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35U.S.C. §120 to U.S. patent application Ser. No. 14/038,388 entitled“HIGH ASPECT RATIO ETCH WITH COMBINATION MASK” filed on Sep. 26, 2013which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of semiconductor devices.More specifically, the invention relates to the etching of high aspectratio features for semiconductor devices.

During semiconductor wafer processing, in 3D flash memory devices,multiple cells are stacked up together in chain format to save space andincrease packing density.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for etching features in a stack is provided.A combination hardmask is formed by forming a first hardmask layercomprising carbon or silicon oxide over the stack, forming a secondhardmask layer comprising metal over the first hardmask layer, andpatterning the first and second hardmask layers. The stack is etchedthrough the combination hardmask.

In another manifestation of the invention, a method for etching featuresin a stack is provided. A combination hardmask is formed by forming afirst hardmask layer comprising carbon or silicon oxide over the stack,forming a second hardmask layer comprising metal over the first hardmasklayer, and forming a patterned mask over the second hardmask layer. Thesecond hardmask layer is etch through the patterned mask by flowing asecond hardmask layer etch gas comprising a halogen component, formingthe second hardmask layer etch gas into a plasma, and stopping the flowof the second hardmask layer etch gas. The first hardmask layer isetched by flowing a first hardmask layer etch gas comprising oxygen andat least one of COS or SO₂, forming the first hardmask layer etch gasinto a plasma, and stopping the flow of the first hardmask layer etchgas. The stack is etched through the combination hardmask.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart of a process that may be used in anembodiment of the invention.

FIGS. 2A-G are schematic cross-sectional views of a memory stack formedaccording to an embodiment of the invention.

FIG. 3 is a more detailed flow chart of a process of patterning thehardmasks that may be used in an embodiment of the invention.

FIG. 4 is a schematic view of a processing chamber that may be used inpracticing the invention.

FIG. 5 illustrates a computer system, which is suitable for implementinga controller used in embodiments of the present invention.

FIG. 6 is a more detailed flow chart of a process of etching the metalhardmask that may be used in an embodiment of the invention.

FIG. 7 is a more detailed flow chart of a process of etching the carbonor silicon oxide hardmask that may be used in an embodiment of theinvention.

FIGS. 8A-C are schematic cross-sectional views of a memory stack formedaccording to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

To facilitate understanding, FIG. 1 is a high level flow chart of aprocess that may be used in an embodiment of the invention. A stack isprovided (step 104). A carbon or silicon oxide containing hardmask isformed over the stack (step 108). A metal containing hardmask is formedover the carbon or silicon oxide containing hardmask (step 112). Thecarbon or silicon oxide containing hardmask and the metal containinghardmask are patterned (step 116). The stack is etched through thepatterned hardmasks (step 120). Patterned hardmasks may include acombination of BARC/DARC/carbon or SiO2.

EXAMPLE

A stack is provided (step 104). In an example of an implementation ofthe invention, 3D memory array is etched. In such a memory array, memorystacks are formed over a wafer. FIG. 2A is a cross sectional view of aplurality of layers of a stack 204 formed over a wafer 208. One or morelayers may be disposed between the stack 204 and the wafer 208. In thisembodiment, the stack 204 is a plurality of memory stacks, which areformed by bilayers of a layer of silicon oxide (SiO₂) 216 on top of alayer of polysilicon 212.

A carbon or silicon oxide hardmask is formed over the stack 204 (step108). FIG. 2B is a cross sectional view of the stack 204 after a carbonor silicon oxide containing hardmask 220 is formed over the stack 204.In this embodiment, the carbon or silicon oxide containing hardmask 220is amorphous carbon.

A metal containing hardmask is formed over the carbon or silicon oxidecontaining hardmask (step 112). FIG. 2C is a cross sectional view of thestack 204 after a metal containing hardmask 224 is formed over thecarbon or silicon oxide containing hardmask 220. In this example, themetal containing hardmask 224 is titanium nitride (TiN).

The hardmasks are patterned (step 116). FIG. 3 is a flow chart of aprocess for patterning the hardmask used in this embodiment of theinvention. A patterned mask is formed over the metal containing hardmask(step 304). FIG. 2D is a cross sectional view of the stack 204 after apatterned mask 228 has been formed over the metal containing hardmask224. In this example, the patterned mask 228 is formed from siliconnitride (SiN).

The stack 204 may be placed in a processing tool to perform subsequentsteps. FIG. 4 is a schematic view of a plasma processing system 400,including a plasma processing tool 401. The plasma processing tool 401is an inductively coupled plasma etching tool and includes a plasmareactor 402 having a plasma processing chamber 404 therein. Atransformer coupled power (TCP) controller 450 and a bias powercontroller 455, respectively, control a TCP supply 451 and a bias powersupply 456 influencing the plasma 424 created within plasma processingchamber 404.

The TCP controller 450 sets a set point for TCP supply 451 configured tosupply a radio frequency signal at 13.56 MHz, tuned by a TCP matchnetwork 452, to a TCP coil 453 located near the plasma processingchamber 404. An RF transparent window 454 is provided to separate TCPcoil 453 from plasma processing chamber 404, while allowing energy topass from TCP coil 453 to plasma processing chamber 404.

The bias power controller 455 sets a set point for bias power supply 456configured to supply an RF signal, tuned by bias match network 457, to achuck electrode 408 located within the plasma processing chamber 404creating a direct current (DC) bias above electrode 408 which is adaptedto receive the wafer 208, being processed.

A gas supply mechanism or gas source 410 includes a source or sources ofgas or gases 416 attached via a gas manifold 417 to supply the properchemistry required for the process to the interior of the plasmaprocessing chamber 404. A gas exhaust mechanism 418 includes a pressurecontrol valve 419 and exhaust pump 420 and removes particles from withinthe plasma processing chamber 404 and maintains a particular pressurewithin plasma processing chamber 404.

A temperature controller 480 controls the temperature of a coolingrecirculation system provided within the chuck electrode 408 bycontrolling a cooling power supply 484. The plasma processing systemalso includes electronic control circuitry 470. The plasma processingsystem 400 may also have an end point detector. An example of such aninductively coupled system is the Kiyo built by Lam Research Corporationof Fremont, Calif., which is used to etch silicon, polysilicon andconductive layers, in addition to dielectric and organic materials. Inother embodiments of the invention, a capacitively coupled system may beused.

FIG. 5 is a high level block diagram showing a computer system 500,which is suitable for implementing a controller used in embodiments ofthe present invention. The computer system may have many physical formsranging from an integrated circuit, a printed circuit board, and a smallhandheld device up to a huge super computer. The computer system 500includes one or more processors 502, and further can include anelectronic display device 504 (for displaying graphics, text, and otherdata), a main memory 506 (e.g., random access memory (RAM)), storagedevice 508 (e.g., hard disk drive), removable storage device 510 (e.g.,optical disk drive), user interface devices 512 (e.g., keyboards, touchscreens, keypads, mice or other pointing devices, etc.), and acommunication interface 514 (e.g., wireless network interface). Thecommunication interface 514 allows software and data to be transferredbetween the computer system 500 and external devices via a link. Thesystem may also include a communications infrastructure 516 (e.g., acommunications bus, cross-over bar, or network) to which theaforementioned devices/modules are connected.

Information transferred via communications interface 514 may be in theform of signals such as electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 514, via acommunication link that carries signals and may be implemented usingwire or cable, fiber optics, a phone line, a cellular phone link, aradio frequency link, and/or other communication channels. With such acommunications interface, it is contemplated that the one or moreprocessors 502 might receive information from a network, or might outputinformation to the network in the course of performing theabove-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon the processors or may executeover a network such as the Internet in conjunction with remoteprocessors that shares a portion of the processing.

The term “non-transient computer readable medium” is used generally torefer to media such as main memory, secondary memory, removable storage,and storage devices, such as hard disks, flash memory, disk drivememory, CD-ROM and other forms of persistent memory and shall not beconstrued to cover transitory subject matter, such as carrier waves orsignals. Examples of computer code include machine code, such asproduced by a compiler, and files containing higher level code that areexecuted by a computer using an interpreter. Computer readable media mayalso be computer code transmitted by a computer data signal embodied ina carrier wave and representing a sequence of instructions that areexecutable by a processor.

Within the plasma processing system 400, the metal containing hardmask224 is etched (step 308). FIG. 6 is a more detailed flow chart of aprocess for etching the metal containing hardmask 224. A metal hardmasketch gas is flowed into the plasma processing chamber 404 (step 604). Inthis example the metal hardmask etch gas is a combination of F and Clcontaining halogen gases mixed with O2, Ar, N2 and He. Halogen gasescould be SF₆, NF₃, Cl₂, CH₂F₂, or C₄F₆. The metal hardmask etch gas isformed into a plasma (step 608). In this example, a pressure in therange of 5-50 mT is provided. Source power from 500-2000 W is providedto form the etch gas into a plasma. A bias voltage of 100-1000 V isprovided. The flow of the metal hardmask etch gas is stopped (step 612).FIG. 2E is a cross sectional view of the stack 204 after features 232have been etched into the metal containing hardmask 224.

The carbon or silicon oxide containing hardmask 220 is etched (step312). FIG. 7 is a more detailed flow chart of a process for etching thecarbon or silicon oxide containing hardmask 220. A carbon or siliconoxide containing hardmask etch gas is flowed into the plasma processingchamber 404 (step 704). In this example the carbon or silicon oxidecontaining hardmask etch gas is CF₄, CH₂F₂, C₄F₆, NF₃, SF₆, Ar, He, andO₂. The carbon or silicon oxide containing hardmask etch gas is formedinto a plasma (step 708). In this example, a pressure in the range of5-50 mT is provided. Source power from 500-2000 W is provided. A biasvoltage 100-1000 V is provided. The flow of the carbon or silicon oxidecontaining hardmask etch gas is stopped (step 712). FIG. 2F is a crosssectional view of the stack 204 after features 232 have been etched intothe carbon or silicon oxide containing hardmask 220.

The stack 204 is etched through the patterned hardmasks (step 120). Anexample of a recipe for etching the stack 204 is provides an etch gascomprising C_(x)H_(y)F_(z), HBr, He, and Ar, if the stack is OPOP, wherex, y, and z are whole numbers. If the stack is ONON, then the etch gascomprises C_(x)H_(y)F_(z), Ar, and He. FIG. 2G is a cross sectional viewof the stack 204 after features 232 have been etched into the stack 204.In this embodiment, during the etching of the stack 204 (step 120), themetal containing hardmask 224 is consumed and the carbon or siliconoxide containing hardmask 220 acts as the mask during the remainder ofthe etching of the stack 204.

Other processes are used to further form the devices. Such processes mayinclude a wet etch that cleans redeposited metal residue. In addition,if the carbon or silicon oxide containing hardmask 220 is carbon, thenan ashing step may be used to remove the carbon or silicon oxidecontaining hardmask 220. Such an ashing process would be less damagingto the stack 204 than a process required to remove the metal containinghardmask 224, if the metal containing hardmask 224 were not removedduring the etch.

This embodiment of the invention increases both the vertical and radialselectivity of the overall mask. The selectivity may be increased by 3to 4 times. Radial selectivity is a function of faceting of the mask. Asthe faceting of the mask increases, the width or radial dimension of theetched feature increases. Therefore, to increase radial selectivity,mask faceting should be reduced. In this embodiment, the metalcontaining hardmask 224 provides the improved selectivity with respectto etching the stack 204. The carbon or silicon oxide containinghardmask 220 acts as a primary buffer during the etching of the stack204 by absorbing the sputtered redeposition of the metal containinghardmask 224 during the etching of the stack 204. The sputtering ismainly from horizontal surfaces of the metal containing hardmask 224.Because the carbon or silicon oxide containing hardmask 220 absorbsredeposited sputtered metal from the metal containing hardmask 224, theresistance to etching of the carbon or silicon oxide containing hardmask220 increases because the sidewalls of the carbon or silicon oxidecontaining hardmask 220 are impregnated with metal, which furtherimproves selectivity. In addition, since the carbon or silicon oxidecontaining hardmask 220 absorbs redeposited sputtered metal, the carbonor silicon oxide containing hardmask 220 reduces or eliminates sputteredmetal from reaching sidewalls of the stack 204, which reduces oreliminates sputtered metal contamination of the stack 204.

In other embodiments, the stack 204 may be a plurality of alternatinglayers of, alternating stacks of silicon oxide and silicon nitride(ONON), alternating stacks of silicon oxide and polysilicon (OPOP), or asingle material such as silicon oxide. The stacks 204 may be used fordifferent uses, such as 3D memory, a 3D NAND, or a DRAM capacitor. Thecarbon or silicon oxide containing hardmask 220 may have a metal dopant.In some embodiments of the invention, in the creation of high aspectratio features, the stacks 204 may have more than 70 alternating layers.More preferably, the stacks 204 have more than 100 alternating layers.In other embodiments, the metal containing hardmask is made of TiOx, W(such as WOx, WN, or WC), or Ta (such as TaN or TaOx).

For etching the metal containing hardmask 224 generally a fluorine orhalogen based etch gas is used to provide a chemical etch. Such an etchmay alternate an etch phase with a passivation phase. For etching acarbon hardmask 220, an oxygen based chemical etch is used. In additionto oxygen, COS or SO₂ are added to the etch gas as a passivant. Theetching of the stack 204 may also be a chemical etch, such as a halogenetch, with a high energy or bias plasma to etch high aspect ratiofeatures. Preferably, such etches are not bombardment type etches. Themetal containing hardmask 224 may be elemental metal, an alloy, a metaloxide, metal nitride, or metal carbide. For etching a stack 204 withsilicon oxide, preferably the carbon or silicon oxide containing stackhardmask 220 is made of carbon. If the stack 204 does not containsilicon oxide, then the carbon or silicon oxide hardmask 220 may besilicon oxide. Preferably, the patterned mask 228 is used to etch boththe metal containing hardmask 224 and the carbon or silicon oxidecontaining hardmask 220. However, in other embodiments, the patternedmask 228 may be used to etch the metal containing hardmask 224, and themetal containing hardmask 224 may be used to etch the carbon or siliconoxide containing mask 220. Such an embodiment might degrade the metalcontaining hardmask 224 while opening the carbon or silicon oxidecontaining hardmask 220.

In another embodiment of the invention, the steps of forming a carbon orsilicon oxide hardmask (step 108) and forming a metal hardmask (step112) are cyclically repeated a plurality of times to form a plurality ofalternating layers of carbon or silicon oxide hardmasks and metalhardmasks. FIG. 8A is a cross sectional view of the stack 804 after aplurality of alternating carbon or silicon oxide containing hardmasks820 and metal containing hardmasks 824 have been formed.

To pattern the hardmasks (step 116), as in the previous embodiment, apatterned mask 828 may be formed (step 304). The steps of etching themetal containing hardmask 824 (step 308) and etching the carbon orsilicon oxide containing hardmask 820 (step 312) are cyclically repeateda plurality of times. FIG. 8B is a cross sectional view of the stack 804after the plurality of alternating carbon or silicon oxide containinghardmasks 820 and metal containing hardmask 824 have been etched using aplurality of cycles of alternating etching the metal containing hardmask824 (step 308) and etching the carbon or silicon oxide containinghardmask 820 (step 312). In this example, the patterned mask 828 isremoved during the etching of the patterning the hardmasks.

The stack 804 is etched through the hardmasks (step 120). The processused in the previous embodiment may be used to etch the stack 804 orother processes may be used. FIG. 8C is a cross sectional view of thestack 804 after features 820 have been etched into the stack 804.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and various substitute equivalentsas fall within the true spirit and scope of the present invention.

What is claimed is:
 1. A method for etching features in a stack,comprising: forming a combination hardmask, comprising; forming a firsthardmask layer comprising carbon or silicon oxide over the stack;forming a second hardmask layer comprising metal over the first hardmasklayer; and patterning the first and second hardmask layers; and etchingthe stack through the combination hardmask.
 2. The method, as recited inclaim 1, wherein the patterning the first and second hardmask layerscomprises: forming a patterned mask over the second hardmask layer;etching the second hardmask layer through the patterned mask; andetching the first hardmask layer.
 3. The method, as recited in claim 2,wherein the etching the second hardmask layer, comprises: flowing asecond hardmask layer etch gas comprising a halogen component; formingthe second hardmask layer etch gas into a plasma; and stopping the flowof the second hardmask layer etch gas; and wherein etching the firsthardmask layer, comprises: flowing a first hardmask layer etch gascomprising oxygen and at least one of COS or SO₂; forming the firsthardmask layer etch gas into a plasma; and stopping the flow of thefirst hardmask layer etch gas.
 4. The method, as recited in claim 3,wherein the second hardmask comprises at least one of elemental metal, ametal alloy, a metal oxide, metal carbide, or a metal nitride.
 5. Themethod, as recited in claim 4, wherein the stack is at least one of asilicon oxide layer, OPOP or ONON.
 6. The method, as recited in claim 5,wherein the forming the combination hardmask, further comprises forminga third hardmask layer comprising carbon or silicon oxide over thesecond hardmask layer, and forming a fourth hardmask layer comprisingmetal over the third hardmask layer.
 7. The method, as recited in claim6, further comprising: etching the fourth hardmask layer, comprising:flowing a fourth hardmask layer etch gas comprising a halogen component;and forming the fourth hardmask layer etch gas into a plasma, andstopping the flow of the fourth; and etching the third hardmask layer,comprising: flowing a third hardmask layer etch gas comprising oxygenand at least one of COS or SO₂; forming the first hardmask layer etchgas into a plasma; and stopping the flow of the first hardmask layeretch gas.
 8. The method, as recited in claim 7, wherein the patterningthe first and second hardmask layers removes the patterned mask.
 9. Themethod, as recited in claim 8, further comprising ashing the firsthardmask layer.
 10. The method, as recited in claim 1, wherein thepatterning the first and second hardmask layers comprises: etching thesecond hardmask layer, comprising: flowing a second hardmask layer etchgas comprising a halogen component; forming the second hardmask layeretch gas into a plasma; and stopping the flow of the second hardmasklayer etch gas; and etching the first hardmask layer, comprising:flowing a first hardmask layer etch gas comprising oxygen and at leastone of COS or SO₂; forming the first hardmask layer etch gas into aplasma; and stopping the flow of the first hardmask layer etch gas. 11.The method, as recited in claim 10, wherein the patterning the first andsecond hardmask layers removes the patterned mask.
 12. The method, asrecited in claim 1, wherein the second hardmask comprises at least oneof elemental metal, a metal alloy, a metal oxide, metal carbide, or ametal nitride.
 13. The method, as recited in claim 1, wherein the stackis at least one of a silicon oxide layer, OPOP or ONON.
 14. The method,as recited in claim 1, wherein the forming the combination hardmask,further comprises forming a third hardmask layer comprising carbon orsilicon oxide over the second hardmask layer, and forming a fourthhardmask layer comprising metal over the third hardmask layer.
 15. Themethod, as recited in claim 14, further comprising: etching the fourthhardmask layer, comprising: flowing a fourth hardmask layer etch gascomprising a halogen component; and forming the fourth hardmask layeretch gas into a plasma; and stopping the flow of the fourth; and etchingthe third hardmask layer, comprising: flowing a third hardmask layeretch gas comprising oxygen and at least one of COS or SO_(2;) formingthe first hardmask layer etch gas into a plasma; and stopping the flowof the first hardmask layer etch gas.
 16. The method, as recited inclaim 1, further comprising ashing the first hardmask layer.
 17. Amethod for etching features in a stack, comprising: forming acombination hardmask, comprising; forming a first hardmask layercomprising carbon or silicon oxide over the stack; forming a secondhardmask layer comprising metal over the first hardmask layer; andforming a patterned mask over the second hardmask layer; etching thesecond hardmask layer through the patterned mask, comprising: flowing asecond hardmask layer etch gas comprising a halogen component; formingthe second hardmask layer etch gas into a plasma; and stopping the flowof the second hardmask layer etch gas; etching the first hardmask layer,comprising: flowing a first hardmask layer etch gas comprising oxygenand at least one of COS or SO₂; forming the first hardmask layer etchgas into a plasma; and stopping the flow of the first hardmask layeretch gas; and etching the stack through the combination hardmask. 18.The method, as recited in claim 17, wherein the second hardmaskcomprises at least one of elemental metal, a metal alloy, a metal oxide,metal carbide, or a metal nitride.
 19. The method, as recited in claim17, wherein the stack is at least one of a silicon oxide layer, OPOP orONON.